Human neurotropic herpes viruses, such as HSV, cause much disease and suffering. The long-term objective of this project is to understand the mechanism of Herpes Simplex Virus latency and reactivation at the molecular level. In the present application, we propose to continue to examine the Latency Associated Transcripts (LATs), and genes in the region of the genome encoding the LATs, to determine what role they play in viral latency and reactivation. These goals will be achieved by using the techniques of molecular virology and a mouse model of infection and latency. In the first specific aim, we will map and characterize transcripts from the region immediately upstream of the LAT promoter. Preliminary evidence suggest that there is a virulence gene encoded in this region. In the second aim, we will study the functionality of the LAT mRNA and 2kb LAT intron. There has been little study of the LAT mRNA, most effort being focused on the 2kb RNA, which is now recognized as an intron. The 2kb LAT intron is found in the nucleus of latently infected neurons, yet in the cytoplasm of lytically-infected cells. What determines the cellular distribution of LAT? The 2kb LAT intron appears in the cytoplasm during lytic infection, yet does not appear to be translated. Does it serve a function like aiding in splicing and export from the nucleus? We will attempt to study LAT function through understanding its structure and the proteins associated with it. In the third specific aim, we will study the mechanism of reactivation and attempt to determine what type of cell factors are involved. Recently, we showed that immediate-early genes do not appear before early genes during reactivation, suggesting that some cellular factor up-regulates, both immediate early and early classes of genes, rather than specifically upregulating immediate-early genes, as is seen during primary infection. These studies will continue our methodical investigation of herpes simplex virus latency and reactivation, and the role of the LAT gene in these processes.